Molecular design of the phenol type extractants

Sergey A Semenov 0 Aleksandr M Reznik 0 0 Lomonosov Moscow State University of Fine Chemical Technology , prospect Vernadskogo, 86, Moscow 119571, Russia A method of optimisation of new extractants structure using the desirable function has been developed. Earlier the desirable function has been proposed by Harrington (Ind Qual Control 21: 494-498, 1965) for the optimisation of processes with several response functions. The developed method of optimisation of new extractants structure has been used for construction of phenolic type extractants (PTE) (a class of N-(2-hydroxy-5-nonylbenzil)-dialkylamines). It has been offered to use the charge on the nitrogen atom, the heat of dissociation of phenolic group, the logarithm of distribution factor of extractant between water and octanol (computed data) and maximum permissible concentration of extractants in aqueous phase (MPC) of the o-replaced phenols (the literary data) as the controllable parameters, defining efficiency of extractants for molecular design of PTE. During optimisation of extractants structure the quantity of alkyl substitutes at nitrogen atom, the carbon atoms number in these substitutes and the electronegative substitutes in o-position to phenolic group have been varied. As the result of the molecular design, the optimal structure of PTE found is N-(2,3-dihydroxy-5-nonylbenzil)-didecylamine, which perfectly meets the requirements to industrial extractants. - Introduction The search and development of new effective extractants are an important scientific and practical issue (Zolotov 1982). There are some requirements to the extractant for metal extraction when using the solvent extraction method. However in practice, it is difficult to find an extractant responsible for all requirements, so one usually compromises and chooses a solution (Ritcey & Ashbrook 1979). The testing of substances, used in other industries as extractants, is of big importance in the expansion of the range of extractants for the extraction of metals (Zolotov 1982). We suggest the use alkyl derivatives of phenols, applied in synthetic rubber industry, plastic industry and elastomers industry, as extractants (Bukin et al. 1999; Bychenkov et al. 2008; Gladikova et al. 2002). However, despite the promise of this idea, it is necessary to consider the fact, that reagents developed for other purposes may not meet to all requirements for extractants. That is why the problem of extractant molecule design, that meets the certain requirements, arises. The computer technology development in recent times allows solving this problem by using calculation methods, like the methods of quantum chemistry or the method of group contributions, etc. The development of a new, more effective extractant allows to reduce expenditures for the rare metals extraction and opens new perspectives in the certain metals usage, that are in limited use because of their high price (for example, scandium) (Korshunov et al. 1987; Komissarova 2006). In the works (Hay 2008; Varnek 2008) in the course of the molecular design of extractants thermodynamic criteria are being considered: the energy of interaction between the receptorion (Hay 2008) and the constants of solvent extraction, distribution coefficients and separation coefficients of extractable metals (Varnek 2008), with the non thermodynamic factors such as MPC (maximum permissible concentration) are not taken into account. The purpose of the current investigation is the development of a method for optimisation the structure of new extractants using the desirability function, proposed earlier by Harrington (1965) for the optimisation of processes, characterised by a few response functions (Ahnazarova & Kafarov 1978). According to Harrington, the desirability function is a dimensionless scale, which allows to convert any C H response so that it is interpreted in the terms of usefulness or desirability for any specific application. For the unilateral restrictions like y ymax or y ymin (yresponse function) a suitable form of the transformation y in d (particular desirability function) is the exponential function: The coefficients b0 and b1 will be determined, if for the two values of given property y one sets the corresponding values of the desirability d, preferably in the range 0.2 < d < 0.8. Having a few responses, converted into d scale, it is possible to combine the generalised desirability Table 1 The values of q and logP for NBAA extractants at varying lengths of two hydrocarbon radicals NB-11, n = 1 NB-22, n = 2 NB-33, n = 3 NB-44, n = 4 NB-55, n = 5 NB-77, n = 7 NB-1010, n = 10 C H C H Figure 2 The substituted in the o-position N-(2-hydroxy-5nonylbenzil)-didecylamine. Methodology The proposed method of the optimisation the structure of new extractants has been used for the designing phenolic type extractants (PTE) (class N-(2-hydroxy-5nonylbenzil)-dialkylamines). Moreover the following controllable parameters were selected: 1. The formal charge on the nitrogen atom (q), as some metals such as scandium (Bychenkov et al. 2008; Gladikova et al. 2002) are extracted by PTE with the formation of chelates and the nitrogen atom inclusion to the chelate cycle. The value of q was calculated by the Milliken approach with the DFT (B3LYP) method, 6-21G basis set using the GAMESS-US (version September 7, 2006) program package. 2. The logarithm of the partition coefficient for n-octanol/water (logP), calculated by means of the group contribution method using the program Chem3D Ultra version 7.0.0, included in the package of applied programs (PAP) ChemOffice Ultra 7.0.1. The value logP allows estimating the solubility of the extractant into the aqua phase and, therefore, the Table 2 The dissociation energy ED, the charge on the nitrogen atom and logP of NBDA- R extractants NBD NO2 NBD F NBD Cl NBD Br NBD I Table 3 The values of o-substituted phenols MPC Substitutes in ortho-position to phenolic group without R (Chernyshev et al. 2005) -Cl (Chernyshev et al. 1999) -NO2 (Chernyshev et al. 2004) -OH (Chernyshev et al. 2004) possible losses of the extractant during the solvent extraction process. 3. The energy of dissociation of the phenolic group (Ed), calculated by the DFT (B3LYP) method, 621G basis set using the GAMESS-US (version September 7, 2006) program package. According to (Gladikova et al. 2002), in the course of scandium solvent extraction by the N-(2-hydroxy-5nonylbenzil)-,-dihydroxyethylamine (NBEA) extractant the optimum pH is 4.5. However, in industrial products containing scandium there is a large amount of iron (III) as a rule (Korshunov et al. 1987), and during the precipitation of iron hydroxide large losses of scandium take place due to co precipitation. So, the problem of PTE designing, which extracts scandium at lower pH, arises. Therefore, the choice of given option is specified by the necessity of increasing the acidity of the phenolic group by introducing electronegative substi (...truncated)